1. If you are in UK and with the vodafone sim card in, you CAN'T DIAL ANY numbers while is in C500, try to call it from other mobile and see if rings, if not, mean phone is BARRED (stolen phone or insurance fraud : ADVICE - Contact your seller AND/OR POLICE!!!).
2. If you can DIAL ANY no, part of ORANGE network no, than that is a REALLY strange one as we never seen such a problem before. ADVICE : please email me the phone no you try to dial so i can try to see WHY is this.
The Imei-Check Team
Yes it only applies to Orange numbers, both my wife and daughter are on Orange and I can't phone iether of them and they can't phone me which is a pain to say the least. I can phone any other number on any other network no problem. When I phone an Orange number I just get three beeps as though the number isn't recognised. When I put the original Orange SIM back into the phone all is OK again. The Vodafone number has been mine for over 18 months now, when I put the Voda SIM in an unlocked Siemens A55 it works fine no problem, which points towards it being a C500 issue with the Voda SIM.
I'm probably stating the obvious, but you HAVE made sure you have a signal etc on the phone?
If you haven't, you might want to try going into Settings > Phone > Network, and manually setting the network to vodafone, and see if that works.
Speaking as an O2 user, my C500 was unlocked by Florin, and I set it up for all the O2 settings, and I can ring, sms, mms, internet and email fine - in and out.
So as far as O2 is concerned, it works fine, so I see no reason why Vodafone shouldn't work.
Just remember, for MMS, Internet, etc Vodafone, you have a whole host of settings to configure first, once you get your actual call problem sorted out.